EFFECT OF CONTROLLED CARBON IMPURITIES ON J(C) IN AG/BI(2223) TAPES

An extensive study of the detrimental effect of C on critical current densities (j(c)) of Ag sheathed Bi(2223) tapes has been carried out. High j(c) can only be obtained if the C content is kept to a minimum. Successive calcination steps at 820-degrees-C are effective in reducing the amount of C in the resulting powders. On the other hand, high energy milling increases the amount of C in the powder. Controlled quantities of C impurities were introduced into the powders by performing the calcinations in a CO2 rich atmosphere. The j(c) measured on tapes obtained with C rich precursors are lower by a factor of 2 to 4 than the j(c) of tapes from powders calcined in air.